package org.example.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/*
 *Author:ZouHeng
 *Des:独占锁，自定义同步组件
 * 同一时刻只允许一个线程占有锁
 *Date:2021-01-04  17:16
 */
public class Mutex implements Lock {
    // 静态内部类，自定义同步器
    private static class Sync extends AbstractQueuedSynchronizer {
        /**
         * 是否处于占用状态
         * @return getState()=1表示被占用，getState()!=1表示未被占用
         */
        protected boolean isHeldExclusively() {
            return getState() == 1;
        }
        // 当状态为0的时候获取锁
        public boolean tryAcquire(int acquires) {
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }
        // 释放锁，将状态设置为0
        protected boolean tryRelease(int releases) {
            if (getState() == 0) throw new
                    IllegalMonitorStateException();
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }
        // 返回一个Condition，每个condition都包含了一个condition队列
        Condition newCondition() { return new ConditionObject(); }
    }

    // 仅需要将操作代理到Sync上即可
    private final Sync sync = new Sync();

    @Override
    public void lock() {
        sync.acquire(1);
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    @Override
    public boolean tryLock() {
        return sync.tryAcquire(1);
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1,unit.toNanos(time));
    }

    @Override
    public void unlock() {
        sync.release(1);
    }

    public boolean isLock(){
        return sync.isHeldExclusively();
    }

    public boolean hasQueuedThreads(){
        return sync.hasQueuedThreads();
    }

    @Override
    public Condition newCondition() {
        return sync.newCondition();
    }
}
